Thread: have i written this program correctly ?

Code:

#include <stdio.h>
#include <stdlib.h>

typedef struct node_s
{
        void *data;
        struct node_s *next;

}node;


int add_to_link_list(node **head)
{
        node *ptr;
        int temp;

        ptr = malloc(sizeof(node));

        if (ptr == NULL)
        {
                fprintf(stderr, "Memory allocation failed\n");
                return (1);
        }

        printf("Enter data\n");
        if (scanf("%d", &temp) != 1)
        {
                fprintf(stderr, "Error while entering data\n");
                return (1);
        }

        ptr->data = malloc(sizeof(int));
        if (ptr->data == NULL)
        {
                fprintf(stderr, "Memory allocation failed\n");
                return (1);
        }

        (int) ptr->data = temp;
        ptr->next = *head;
        *head = ptr;

        return (0);
}

int main(void)
{
        node *head = NULL;
        node *ptr;
        int n, i;

        printf("How many numbers\n");
        if (scanf("%d", &n) != 1)
        {
                fprintf(stderr, "Error while enterning list size\n");
                return (EXIT_FAILURE);
        }

        for (i = 0; i < n; i++)
        {
                if (add_to_link_list(&head))
                {
                        fprintf(stderr, "add_to_link_list failed\n");
                        return (EXIT_FAILURE);
                }
        }

        ptr = head;

        while (ptr != NULL)
        {
                printf("%d\n", ptr->data);
                ptr = ptr->next;
        }

        return (EXIT_SUCCESS);
}

btw i didn't understand how the statement

printf("%d\n", ptr->data) was acceptable. The compiler did not warn me to do a typecast or anything. Can I get away witht his while using scanf as well ? scanf("%d", &ptr->data) ?

This is what your compiler should have told you:

Code:

temp.c: In function `add_to_link_list':
temp.c:39: warning: use of cast expressions as lvalues is deprecated
temp.c: In function `main':
temp.c:72: warning: int format, pointer arg (arg 2)

Originally Posted by tabstop

This is what your compiler should have told you:

Code:

temp.c: In function `add_to_link_list':
temp.c:39: warning: use of cast expressions as lvalues is deprecated
temp.c: In function `main':
temp.c:72: warning: int format, pointer arg (arg 2)

I changed my program to the following and its working perfectly well :

Code:

#include <stdio.h>
#include <stdlib.h>

typedef struct node_s
{
        void *data;
        struct node_s *next;

}node;


int add_to_link_list(node **head)
{
        node *ptr;
        int temp;

        ptr = malloc(sizeof(node));

        if (ptr == NULL)
        {
                fprintf(stderr, "Memory allocation failed\n");
                return (1);
        }

        ptr->data = malloc(sizeof(int));
        if (ptr->data == NULL)
        {
                fprintf(stderr, "Memory allocation failed\n");
                return (1);
        }

        printf("Enter data\n");
        if (scanf("%d", &ptr->data) != 1)
        {
                fprintf(stderr, "Error while entering data\n");
                return (1);
        }
        
        ptr->next = *head;
        *head = ptr;

        return (0);
}

int main(void)
{
        node *head = NULL;
        node *ptr;
        int n, i;

        printf("How many numbers\n");
        if (scanf("%d", &n) != 1)
        {
                fprintf(stderr, "Error while enterning list size\n");
                return (EXIT_FAILURE);
        }

        for (i = 0; i < n; i++)
        {
                if (add_to_link_list(&head))
                {
                        fprintf(stderr, "add_to_link_list failed\n");
                        return (EXIT_FAILURE);
                }
        }

        ptr = head;

        while (ptr != NULL)
        {
                printf("%d\n", ptr->data);
                ptr = ptr->next;
        }

        return (EXIT_SUCCESS);
}

Define "perfectly well". Your print statements should be printing, not garbage necessarily, but not actual values.

Originally Posted by tabstop

Define "perfectly well". Your print statements should be printing, not garbage necessarily, but not actual values.

They print actual values correctly.

I'm using digital mars compiler and used the -a option(strict ansi c/c++) and got no warnings or errors.

Somehow, you're still suppressing warnings (i.e., you have a valid program, but it doesn't do what you think it does) -- and here you have two warnings that cancel out:

Code:

temp.c: In function `add_to_link_list':
temp.c:33: warning: int format, pointer arg (arg 2)
temp.c:15: warning: unused variable `temp'
temp.c: In function `main':
temp.c:71: warning: int format, pointer arg (arg 2)

So your pointer isn't valid, you're storing the value of the integer as the value of the pointer.

yes, i realised that error.

Code:

#include <stdio.h>
#include <stdlib.h>

typedef struct node_s
{
        void *data;
        struct node_s *next;

}node;


int add_to_link_list(node **head)
{
        node *ptr;
    
        ptr = malloc(sizeof(node));
        if (ptr == NULL)
        {
                fprintf(stderr, "Memory allocation failed\n");
                return (1);
        }

        ptr->data = malloc(sizeof(int));
        if (ptr->data == NULL)
        {
                fprintf(stderr, "Memory allocation failed\n");
                return (1);
        }

        printf("Enter data\n");
        if (scanf("%d", ptr->data) != 1)
        {
                fprintf(stderr, "Error while entering data\n");
                return (1);
        }
        
        ptr->next = *head;
        *head = ptr;

        return (0);
}

int main(void)
{
        node *head = NULL;
        node *ptr;
        int n, i;
        int *temp;
        
        printf("How many numbers\n");
        if (scanf("%d", &n) != 1)
        {
                fprintf(stderr, "Error while enterning list size\n");
                return (EXIT_FAILURE);
        }

        for (i = 0; i < n; i++)
        {
                if (add_to_link_list(&head))
                {
                        fprintf(stderr, "add_to_link_list failed\n");
                        return (EXIT_FAILURE);
                }
        }

        ptr = head;
      
        while (ptr != NULL)
        {
                temp = (int *)ptr->data;
                printf("%d\n",*temp);
                ptr = ptr->next;
        }

        return (EXIT_SUCCESS);
}